The use of optical fibers as a means of transferring information has become increasingly more widerspread because of advantages over conventional wire transmission means such as very high informaion carrying capacity and improved resistance to external interference. Such industries as telecommunications, computer links, and data base access are among the fields which are making increasing use of optical fibers.
Optical fibers are produced by heating a petreated or preformed glass or quartz rod to its softening point, which generally is in excess of 1600.degree. C., and drawing a thin strand from the rod which cools to become optical fiber.
The purity of the optical fiber is very important for the attainment of its advantageous high carrying capacity. One very serious source of impurities is the ambient air which can impart impurities to the drawn fiber. In order to mitigate this potential problem those skilled in the art coat newly drawn optical fibers with a barrier, such as a polymer coating, which serves to keep airborne impurities from containing the optical fiber.
Another potential problem with optical fibers is their lack of structural strength due primarily to their very thin diameters. Stress faults in an optical fiber can also cause a sharp diminution in their information carrying capacity. Fortunately the aforementioned barrier coating can also serve as a structural support for the optical fiber.
As mentioned previously the temperature of optical fiber is at least about 1600.degree. C. as it is being drawn. However the temperatures of the optical fiber must be below about 90.degree. C. when the barrier coating is applied because at temperature above about 90.degree. C. the coating meniscus collapses resulting in a non-uniform coating thickness and a potentially ineffective coating.
One way to cool the optical fiber is to draw it through a long distance from the originating rod to the coating operation. However this method is disadvantageous because it is time consuming, takes up valuable production space, and subjects the optical fiber to contamination and stress through the long distance.
Another way to cool the optical fiber is to pass it through a cryogenic gas. However, because of the relatively small heat capacity of the gas, the cooling rate is still not very high and therefore it still takes a relatively long time, and also a large amount of cryogenic gas to cool the optical fiber to the requisite temperature for coating.
Yet another method for cooling optical fiber is to pass the optical fiber in contact with liquid quenchant. This method sharply decreases the required cooling time but has the disadvantage of the potential for mechanical interference with the optical fiber causing a compromise in its structural integrity. This is because the density of the liquid is high and may approach that of the optical fiber. This problem does not arise with the use of cryogenic gas as coolant because of the relatively low density of the cryogenic gas.
It is therefore desirable to have a process and apparatus which can rapidly cool an optical fiber without interfering substantially with its structural integrity.
It is an object of this invention to provide a method and apparatus for the rapid cooling of optical fiber by the use of cryogenic gas as the coolant.